Windows/Mac/Linux (Adobe Air): Klok, a free time and project-tracking app for the Adobe Air platform, is a great time-tracking solution for multi-platform users, as well as anyone who likes to keep it simple. Simple projects allow you to simply create and describe time entries on a drag-and-adjust grid, or use a template like "Web project" to automatically create sub-categories of HTML, design, text, and the like. You can also use Klok as a work timer using the "Work On" button, and export reports and invoices for clients. Klok is a free download for any system running the Adobe Air platform.